1. Field of the Invention
The present invention relates to an endoscope in which a first cylindrical member configuring an elongated insertion portion to be inserted into a subject and a second cylindrical member are coupled by a connecting member.
2. Description of the Related Art
In recent years, endoscopes have come into widespread use in a medical field and an industrial field. With an endoscope used in the medical field, an elongated insertion portion is inserted into a body cavity of a subject to observe an organ in the body cavity, or to perform various treatments using a treatment instrument that is inserted into a channel included in the endoscope as necessary.
In addition, with an endoscope used in the industrial field, an elongated insertion portion of the endoscope is inserted into an object such as a jet engine and piping in a factory to perform inspection such as observation of a flaw, a corrosion, and the like of a portion to be examined in the object and various measures.
The insertion portion of the endoscope has a well-known configuration including a distal end portion that is positioned at a distal end of the insertion portion in an inserting direction (hereafter, simply referred to as a distal end) and that is provided therein with an image pickup unit for picking up an image of a subject, a bending portion that is provided being connected to a proximal end in the inserting direction of the distal end portion (hereafter, simply referred to as a proximal end) and that is bendable in a plurality of directions, and a flexible tube portion that is elongated and has flexibility and that is provided being connected to the proximal end of the bending portion.
Here, a well-known configuration includes a connecting member used for connecting the proximal end of the bending portion and the distal end of the flexible tube portion.
FIG. 19 is a partial cross sectional view showing a conventional connection configuration between the proximal end of a bending portion and the distal end of a flexible tube portion. Japanese Patent Application Laid-Open Publication No. 2012-95719 discloses, as shown in FIG. 19, a configuration in which the proximal end of a bending portion 120 and the distal end of a flexible tube portion 130 are connected using a connecting member 150 that is folded into a crank-shape at a halfway position in an inserting direction S (hereafter, simply referred to as a halfway position).
More specifically, as shown in FIG. 19, the connecting member 150 is formed into a cylindrical shape, and includes a crank portion 150c formed at the halfway position. In the connecting member 150, this causes a distal end side portion 150s that is positioned closer to a distal end side in the inserting direction S (hereafter, simply referred to as a distal end side) than the crank portion 150c, to be positioned inside the insertion portion in a radial direction K as compared with a proximal end side portion 150k that is positioned closer to a proximal end side in the inserting direction (hereafter, simply referred to as a proximal end side) than the crank portion 150c. 
In addition, the bending portion 120 is configured on the outer circumference of the distal end side portion 150s of the connecting member 150, and the outer circumference of the distal end side portion 150s is covered with a bending cover 120g being a second covering member. In addition, a bending piece 120e is fixed that is positioned at the most rearward (hereafter, referred to as rearward) position in the inserting direction S out of a plurality of bending pieces 120k being second cylindrical members that are covered with the bending cover 120g. Note that the respective proximal ends of the bending piece 120e and the bending cover 120g are caused to abut the distal end of the crank portion 150c of the connecting member 150.
Furthermore, on the inner circumference of the proximal end side portion 150k of the connecting member 150, a distal end side of a braid 130b is fixed to an inner circumferential portion being a first cylindrical member that configures the flexible tube portion 130 and a flex 130f having a cylindrical shape is fixed to the braid 130b (hereafter, the braid 130b whose inner circumference is fixed to the flex 130f will be referred to as a flexible member 130n). Note that the distal end of the flexible member 130n is caused to abut the proximal end of the crank portion 150c of the connecting member 150.
In addition, the distal end side of an outer sheath 130g being a first covering member that covers the outer circumference of the braid 130b is fixed on the outer circumference of the proximal end side portion 150k of the connecting member 150, being caused to abut the proximal end of the bending cover 120g. 
In addition, although not shown in Japanese Patent Application Laid-Open Publication No. 2012-95719, in order to secure water-tightness of the connecting portion between the proximal end of the bending portion 120 and the distal end of the flexible tube portion 130 after coupling the bending portion 120 and the flexible tube portion 130 using the connecting member 150, as shown in FIG. 19, a binding thread 160 is normally wound on the outer circumference on the proximal end side of the bending cover 120g and on the outer circumference on the distal end side of the outer sheath 130g. Furthermore, an adhesive 170 is applied so as to cover the binding thread 160, and a gap between the proximal end of the bending portion 120 and the distal end of the flexible tube portion 130. That is, configurations subjected to so-called thread winding and bonding are well-known.
In addition, the distal end side of the outer sheath 130g is fixed on the outer circumference of the braid 130b in such a manner that the distal end of the outer sheath 130g abuts the proximal end of the proximal end side portion 150k of the connecting member 150. In addition, conceivable configurations include one in which the reduction of the outer diameter of the above-described fixed portion is achieved by performing the thread winding and bonding not only on the outer circumference on the proximal end side of the bending cover 120g, but also on the outer circumference of the proximal end side portion 150k of the connecting member 150 and on the outer circumference on the distal end side of the outer sheath 130g. 
Furthermore, conceivable configurations include one in which the reduction is achieved and the connecting operation is simplified by securing water-tightness of the above-described connecting portion with only the adhesive 170, without using the binding thread 160.